Chapter 15 – Stars, Galaxies and the Universe

1. Chapter 15 – Stars, Galaxies and the Universe

2. Chapter 15 – History of the Universe • Section 2 – Characteristics of Stars Standards • 4.b – Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature and color • 4.c – Students know how to use astronomical units and light years as measures of distance between the Sun, stars and Earth

3. Classifying Stars • Characteristics used to classify stars include color, temperature, size, composition and brightness • Color – red, red-orange, yellow, white, blue • Temperature – ranges from 3,000 to 50,000 • Size – super giant, giant, medium, dwarf, neutron • Composition – what makes up the star (elements) • Brightness – how much light it gives off

4. Star Size • Stars vary greatly in size. Giant stars are typically 10 to 100 times larger than the sun and more than 1,000 times the size of a white dwarf.

5. Star Comparison

6. Star Spectrums • Astronomers can use line spectrums to identify the chemical elements in a star. Each element produces a characteristic pattern of spectral lines. Hydrogen Helium Sodium Calcium

7. Brightness of Stars • The brightness of a star depends on both its size and temperature • Apparent Magnitude – brightness of a star as seen from earth • Absolute Magnitude – the brightness a star would have if it were at a standard distance from earth (all stars same distance)

8. Distances to Stars • Astronomical Unit (AU) – the average distance from Earth to the sun (150 million kilometers or 93 million miles) • Light-year – distance light travels in one year about 9.5 million million kilometers

9. Measuring Distances to Stars • Astronomers often use parallax to measure distances to nearby stars.

10. Measuring Distances to Stars • Astronomers measure how much a star appears to move against a background of stars that are much farther away. Less movement means the star is further away.

11. Hertzsprung-Russell Diagram • HR Diagram plots stars on a graph with axes of brightness, temperature and color • Main Sequence – 90% of all stars; forms the diagonal line on the H-R Diagram

13. Chapter 15 – Stars, Galaxies and the Universe • Section 3 – Lives of Stars Standards • 4.b – Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature and color • 4.d – Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light

14. A Star is Born • Nebula – large amount of gas and dust spread out in immense volume. • A star is born when the contracting gas and dust from a nebula become so dense and hot that nuclear fusion starts • Protostar – earliest stage of a stars life

15. Lifetimes of Stars • How long a star lives depends on its mass • Small stars use up their fuel more slowly than large stars, so they have much longer lives • Medium-mass stars (like the sun) live for about 10 billion years … Astronomers think the sun is about 4.6 billion years old, about half way through its lifetime

16. Deaths of Stars • After a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole. • Planetary Nebulas – a huge cloud of gas that is created when the outer layers of a red giant star drift out into space

17. Deaths of Stars • White dwarfs – product of the death of a small to medium star…about half the size of Earth, with about as much mass as the sun • Supernova – when a dying giant or supergiant star suddenly explodes • Neutron stars – smaller and more dense than white dwarfs

18. Deaths of Stars • Black Holes – form when the most massive stars die – (40 times the mass of the sun) • Pulsar – a rapidly spinning neutron star that produces radio waves

19. The Lives of Stars • A star’s life history depends on its mass. After a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole. Low/Med mass protostar – Low/Med mass star – Red Giant Planetary nebula – White dwarf

20. The Lives of Stars • A star’s life history depends on its mass. After a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole. High mass protostar – High mass star – SuperGiant Supernova – Neutron star or Black Hole